Heat exchanger and method of making thereof

ABSTRACT

A heat exchanger includes an inner tube extending longitudinally along a central axis and having an inner surface bounding a product chamber and an outer surface having a plurality of channels disposed at circumferentially spaced intervals in alternating relationship with a plurality of fins about the circumference of the outer surface of the inner tube; and a longitudinally extending outer tube disposed coaxially about and circumscribing the inner tube in radially spaced relationship, the outer tube having an inner surface contacting the plurality of fins of the inner cylinder, the outer surface being welded to the fins at a plurality of weld locations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/356,427, filed May 6, 2014, which is an U.S. National Stageapplication under 35 USC 371 of international application serial numberPCT/US2012/062358, filed Oct. 29, 2012, which claims the benefit of U.S.provisional patent application Ser. No. 61/556,987 filed Nov. 8, 2011,the entire contents of which are incorporated herein by reference.

FIELD OF INVENTION

This invention relates generally to heat exchangers for freezing anddispensing semi-frozen products and, more particularly, to an improvedheat exchanger for removing heat from the product within the productfreezing chamber of the dispensing apparatus.

DESCRIPTION OF RELATED ART

Soft-serve ice cream, yogurt, custard and other semi-frozen foodproducts, as well as semi-frozen drinks, sometimes referred to asslushes, are commonly dispensed through a dispensing apparatus having aheat exchanger in the form of a freezing cylinder. The freezingcylinder, also referred to as a freezing barrel, defines alongitudinally elongated freezing chamber. Typically, unfrozen liquidproduct mix is added to the freezing chamber at the aft end of thefreezing cylinder and selectively dispensed at the forward end of thefreezing cylinder through a manually operated dispensing valve. Arotating beater, typically formed by two or more helical blades drivenby a drive motor at a desired rotational speed, scrapes semi-frozenmixture from the inner wall of the freezing cylinder and moves theproduct forwardly through the freezing chamber defined within thefreezing cylinder as the product transition from a liquid state to asemi-frozen state. The product within the freezing chamber changes froma liquid state to a semi-frozen state as heat is transferred from theproduct to a refrigerant flowing through an evaporator disposed aboutthe freezing cylinder. The evaporator is operatively associated with andpart of a conventional refrigeration system that also includes acompression device and a refrigerant condenser arranged in aconventional refrigerant cycle in a closed refrigerant circuit.Dispensing apparatus of this type may have a single freezing cylinderfor dispensing a single flavor of product or a plurality of freezingcylinders, each housing a selected flavor of product, for dispensingeach of the selected flavors and even a mix of flavors.

As noted previously, heat is removed from the product within thefreezing cylinder and carried away by a refrigerant circulating throughan evaporator disposed about the freezing cylinder. In dispensingapparatus having more than one freezing cylinder, an evaporator isdisposed about each freezing cylinder. In conventional apparatus fordispensing semi-frozen products, the evaporator is typically configuredeither as a tube wound around and in contact with the outside wall ofthe freezing cylinder or as an annular chamber from between the outsidewall of the freezing cylinder and the inside wall of an outer cylinderdisposed coaxially about the freezing cylinder. Published internationalpatent publication WO2010/151390 discloses a freezing cylinder having anevaporator including a plurality of channels disposed about the outersurface of an inner cylinder. While this design is well suited for itsintended purposes, improvements in such freezing cylinders would be wellreceived in the art.

BRIEF SUMMARY

According to an example embodiment of the present invention, a heatexchanger includes an inner tube extending longitudinally along acentral axis and having an inner surface bounding a product chamber andan outer surface having a plurality of channels disposed atcircumferentially spaced intervals in alternating relationship with aplurality of fins about the circumference of the outer surface of theinner tube; and a longitudinally extending outer tube disposed coaxiallyabout and circumscribing the inner tube in radially spaced relationship,the outer tube having an inner surface contacting the plurality of finsof the inner cylinder, the outer surface being welded to the fins at aplurality of weld locations.

According to another example embodiment of the present invention, amethod of making a heat exchanger includes obtaining an inner tubeextending longitudinally along a central axis and having an innersurface bounding a product chamber and an outer surface having aplurality of channels disposed at circumferentially spaced intervals inalternating relationship with a plurality of fins about thecircumference of the outer surface of the inner tube; positioning anouter tube over the inner tube, the outer tube being disposed coaxiallyabout and circumscribing the inner tube in radially spaced relationship,the outer tube having an inner surface contacting the plurality of finsof the inner cylinder; and welding the outer tube to the inner tube at aplurality of weld locations.

Other aspects, features, and techniques of the invention will becomemore apparent from the following description taken in conjunction withthe drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 is a schematic diagram illustrating an exemplary embodiment of anapparatus for freezing and dispensing a semi-frozen product embodyingthe invention;

FIG. 2 is a perspective view of an exemplary embodiment of a freezingbarrel in accordance with the invention;

FIG. 3 is a perspective view of an exemplary embodiment of the innercylinder of the freezing barrel of FIG. 2;

FIG. 4 is a sectioned side elevation view of the inner cylinder of FIG.3;

FIG. 5 is a cross-sectional elevation view of the inner cylinder of FIG.3 taken along line 5-5 with the outer cylinder assembledcircumferentially about the inner cylinder;

FIG. 6 is a magnified view of a segment of the freezing barrel definedwithin line 6-6 of FIG. 5;

FIG. 7 is a magnified view of a segment of another embodiment of afreezing barrel in accordance with an aspect of the invention;

FIG. 8 depicts a welded heat exchanger in an exemplary embodiment; and

FIG. 9 depicts a welded heat exchanger in another exemplary embodiment.

DETAILED DESCRIPTION

Referring initially to FIG. 1, there is depicted schematically anexemplary embodiment of an apparatus 10 for freezing and dispensingsemi-frozen food products, such as by way of example, but not limitedto, soft-serve ice cream, ice milk, yogurt, custard, shakes, carbonatedand/or non-carbonated ice slush drinks, that embodies the presentinvention.

In the depicted embodiment, the apparatus 10 includes two freezingchambers C1 and C2 for dispensing food products of different flavors ortypes. The freezing chambers C1 and C2 are defined within the axiallyelongated cylindrical barrels 20-1 and 20-2, respectively. Althoughshown as a dual barrel dispenser, it is to be understood that theapparatus 10 may have only a single barrel machine for dispensing asingle product or may have three or more barrels for dispensing aplurality of flavors or types of products or a mix of flavors. Each ofthe barrels 20-1, 20-2 includes and inner cylinder 30, an outercylindrical 40 circumscribing the inner cylinder 30 and an evaporator 50formed between the inner cylinder 30 and the outer cylinder 40.Refrigerant is supplied from a refrigeration system 60 to theevaporators 50 of the respective barrels 20-1, 20-2 for refrigeratingproduct resident within the respective freezing chambers C1 and C2.

A beater 22 is coaxially disposed and mounted for rotation within eachof the chambers C1 and C2. Each beater 22 is driven by a drive motor 23to rotate about the axis of its respective one of the barrels 20-1,20-2. In the embodiment depicted in FIG. 1, a single drive motor, whenenergized, simultaneously drives each of the beaters 22 in rotationabout the axis of its respective barrel. However, it is to be understoodthat each beater 22 may be driven by a motor dedicated solely to drivingthat respective beater. A respective product supply 24 is operativelyassociated with each of the barrels 20-1, 20-2 for supplying product tobe frozen to the respective chamber C1 and C2 with which the productsupply is associated. The apparatus 10 is also equipped with adispensing valve system that is selectively operable for dispensing thesemi-frozen product from the barrels in a manner well known in the art.

The refrigeration system 60 includes a single refrigerant vaporcompressor 62 driven by a compressor motor 65 operatively associatedwith the compressor 62, and condenser 64 connected with the evaporators50 in a refrigerant circuit according to refrigeration cycle. It isunderstood that multiple compressors may be used, with an individualcompressor designated for each evaporator. The compressor 62 isconnected in refrigerant flow communication by high pressure outlet line61 connected to the refrigerant inlet to the condenser 64 and therefrigeration outlet of the condenser 64 is connected through a highpressure refrigerant supply line 63 to refrigerant flow control valves66, one of which being operatively associated with one of theevaporators 50 of barrel 20-1 and the other being operatively associatedwith the other of the evaporators 50 of barrel 20-2. Each of the valves66 is connected by a respective refrigerant line 67 to the refrigerantinlet of the respective evaporator 50 associated therewith. A respectiverefrigerant outlet of each evaporator 50 is connected through a lowpressure refrigerant return line 69 and an accumulator 68 to the suctionside of the compressor 62. The refrigerant flow control valves 66 may,for example, comprise on/off solenoid valves of the type which can berapidly cycled between an open position passing flow of refrigerant toan associated evaporator 50 and a closed position blocking flow ofrefrigerant to an associated evaporator. The valves 66 may beimplemented using a variety of devices including, but not limited to,pulse width modulated solenoid valves, electronic motor operated valves,automatic expansion valves, thermal expansion valves, ejectors, etc.Valves 74 and 76 connect the compressor outlet directly to evaporators50 to enable hot gas heating of product in barrels 20-1 and 20-2. Fourway valve 78 allows the system to run in a reverse gas mode, where theevaporators 50 serve as condensers, the heat product in barrels 20-1 and20-2.

Different products have different thermal transfer rates and differentfreezing points. Therefore, operation of the refrigeration system 60will vary dependent upon the products being supplied to the freezingchambers C1 and C2. Operation of the refrigeration system 60 may becontrolled by a control system 70 that controls operation of thecompressor drive motor 65, the beater motor 23, and the flow controlvalves 66. The control system 70 includes a programmable controller 72that includes a central processing unit with associated memory, inputand output circuits, and temperature sensors for sensing the temperatureof the product within the chambers C1 and C2. For a more thoroughdiscussion of the design and operation of an exemplary control system 70reference is made to U.S. Pat. No. 5,205,129, the disclosure of which ishereby incorporated by reference in its entirety.

In the depicted embodiment, each barrel 20 is equipped with aselectively operable dispensing valve 11 disposed at the forward end ofthe barrel 20 for receiving product from the freezing chamber. However,as in some conventional dual barrel dispensers, the dispensing valvesystem may include a third dispensing valve selectively operable todispense a mix of the two flavors or types of products present in themixing chambers C1 and C2. The dispensing valve system may also comprisea single selectively operable valve that is selectively positionable ina first position to dispense product from chamber C1 only, in a secondposition to dispense product from chamber C2 only, and in a thirdposition to dispense mix of the products from both chambers C1 and C2.

Briefly, in operation, product to be frozen is supplied to each of thechambers C1 and C2 from the respective product supply 24 associatedtherewith from a supply tube 27 opening into the chamber at the aft endof each barrel 20. The product supplies 24 are arranged, as inconventional practice, to feed as required a liquid comestible productmix and generally, but not always, an edible gas, such as for example,air, nitrogen, carbon dioxide or mixtures thereof, in proportions toprovide a semi-frozen food product having the desired consistency. Theliquid comestible product mix may be refrigerated by suitable apparatus(not shown) to pre-cool the product mix to a preselected temperatureabove the freezing temperature of the product mix prior to delivery tothe chambers C1 and C2. The beaters 22 rotates within its respectivechamber C1, C2 so as churn the product mix resident within the chamberand also move the product mix to the forward end of the chamber fordelivery to the dispensing valve 11. The blades of the beaters 22 mayalso be designed to pass along the inner surface of the inner cylinder30 as the beater rotates so as to scrape product from the inner surfaceof the inner cylinder 30. As the product mix churns within the chambersC1 and C2, the product mix is chilled to the freezing point temperatureto produce a semi-frozen product ready-on-demand for dispensing. If gasis added to the product mix, the gas is thoroughly and uniformlydispersed throughout the product mix as the beaters rotate.

Referring now to FIGS. 2-6, in particular, each freezing barrel 20includes an inner tube 30, an outer tube 40 circumscribing the innertube 30 and an evaporator 50 formed between the inner tube 30 and theouter tube 40. The inner tube 30 comprises a cylinder extendinglongitudinally along a central axis 31 and having an inner surfacebounding the freezing chamber C and an outer surface 34. The outer tube40 comprises a cylinder extending longitudinally along the axis 31 andcoaxially circumscribing the longitudinally extending inner cylinder 30.The outer tube 40 has an inner surface 42 facing the outer surface 34 ofthe inner cylinder 30. The inner tube 30 may be made from food gradestainless steel or other metal approved for use in connection in foodprocessing applications. A product supply tube 27 opens into thefreezing chamber C through a first end of the inner cylinder 30 of thebarrel 20, which end is also referred to herein as the feed end or aftend. The dispensing valve 11 is disposed at the axially opposite end ofthe barrel 20, which end is also referred to herein as the discharge endor forward end.

The outer surface of the inner tube 30 is provided with a plurality offins 52 and a plurality of channels 53 disposed at circumferentiallyspaced intervals in alternating relationship with a plurality of fins 52about the circumference of the outer surface of the inner tube 30. Thefins 52 and channels 53 may be formed integrally with the shell of thefirst tube 30, for example, by machining material from the outer surfaceof the inner cylinder 30 thereby simultaneously forming the channels 53and the fins 52 that alternate with and extend radially outwardlybetween channels 53. The inner tube could also be formed with the fins52 being made integral therewith by extrusion. In an embodiment, theinner tube 30 has an outer shell diameter that nearly matches the insideshell diameter of the outer tube 40, such that when the channels 53 aremachined in the outer surface 34 of the inner tube 30 thereby formingthe plurality of the fins 52 of the inner tube 30, the fins 52 extendradially outwardly to abut the inner surface 42 of the outer tube 40when the barrel 20 is assembled by slip fitting the outer tube 40 overthe inner tube 30.

The outer surface 34 of the inner tube 30 is also provided with a firstrecess 56 and a second recess 58 formed in and extendingcircumferentially about the outer surface 34 of the inner tube 30 atlongitudinally spaced end regions of the inner tube 30. In the depictedexemplary embodiment the first recess 56 is at the product discharge endof the inner tube 30 and the second recess 58 is at the product feed endthereof. The first tube 30 has at least one inlet 57 opening to firstrecess 56 for receiving refrigerant from the refrigerant system 60 andhas at least one outlet 59 opening to the second recess 58 for returningrefrigerant to the refrigerant system 60. In the exemplary embodimentdepicted in FIGS. 3-6, four refrigerant inlets 57 are provided atequally spaced circumferential intervals about the first recess 56 andfour refrigerant outlets 59 are provided at equally spacedcircumferential intervals about the second recess 58.

Each channel 53 forms a refrigerant flow passage that extends betweenand establishes fluid flow communication between the first recess 56 andthe second recess 58. In the depicted embodiment, each channel 53 of theplurality of channels extends longitudinally parallel to the axis 31 ofthe inner tube 30 between the first recess 56 and the second recess 58.Thus, the first recess 56 forms a refrigerant inlet header and thesecond recess forms a refrigerant outlet header which together with thechannels 53 formed in the inner tube 30, in assembly with the outer tube40, provides a heat exchanger, which in the embodiment described hereindefines the evaporator 50 of the freezing barrel 20 through whichrefrigerant is circulated in heat exchange relationship with the productresident within the freezing chamber C bounded by the inner surface ofthe inner tube 30 for chilling the product resident therein. The firstrecess 56 is connected in fluid flow communication via at least oneinlet 57 with the refrigerant supply line 63 through valve 66 and line67 to receive refrigerant into the evaporator 50, while the secondrecess 58 is connected in fluid flow communication via at least oneoutlet 59 with the refrigerant line 69 for passing refrigerant from theevaporator 50. In the depicted embodiment, four inlets 57 are providedto the first recess 56 at circumferentially spaced intervals of ninetydegrees. Similarly, four outlets 59 are provided to the second recess 58at circumferentially spaced intervals of ninety degrees.

In an embodiment, each channel 53 of the plurality of channels ismachined into the outer surface of the inner tube 30 to define a flowpassage having a desired cross-section shape, such as for example agenerally rectangular or square cross-sectional shape. The channels 53may be machined into the outer surface of the inner tube 30.Additionally, each channel 53 may be machined to a desired depth and adesired width to provide a flow passage having a desired hydraulicdiameter. In an embodiment, each of the channels defines a flow passagehaving a cross-sectional flow area having a hydraulic diameter in therange of about 0.02 inch to 0.10 inch (about 0.50 millimeter to 2.54millimeters). For example, in an embodiment, each of the channels 53 maybe machined to have a depth of 0.0625 inch (1.5875 millimeters) and awidth of 0.0625 inch (1.5875 millimeters) thereby defining a flowpassage having a cross-sectional flow area having a hydraulic diameterof about 0.0625 inch (1.5875 millimeters). The plurality of channels 53may be disposed at circumferentially equally spaced intervals about thecircumference of the inner cylinder. For example, in an exemplaryapplication of the semi-frozen product dispensing apparatus 10, an innertube 30 of a freezing barrel 20 having an outer shell diameter of 4.1inches (104 millimeters), a total of 128 equally circumferentiallyspaced channels 53 might be disposed about the circumference of theouter surface of the inner cylinder 30.

In an embodiment, as depicted in FIG. 7, the evaporator 50 is extrudedas an integral member having a plurality of channels 53 disposed atspaced intervals about the evaporator 50. In the extrusion process, thechannels 53 are formed between fins 52 that are formed integrally withand extend between a pair of spaced walls. The evaporator 50 may beformed in the flat and rolled into a cylindrical shape with the fins 52extending radially or extruded in a cylindrical shape with the fins 52extending radially. The cylindrically formed evaporator 50 is themassembled over the inner tube 30, as illustrated in FIG. 7, and brazedor soft-soldered in place over the outer surface of the inner tube 30.Since the structure of the extruded evaporator 50 provides forcontainment of the pressure of the refrigerant passing through thechannels 53, no outer shell is required. Further, the inner tube 30 doesnot need to be designed to contain the high pressure of the refrigerantflowing through the evaporator 50 and may be made of a thinner thicknessstainless steel than would be required in the case where the inner tube30 forms a part of the refrigerant containment structure. In alternateembodiments, the evaporator 50 is made from an aluminum extrusion. Thealuminum extrusion may be plated with copper and brazed to inner tube30. Alternatively the extruded aluminum evaporator 50 may have itsinside surface plated with nickel to provide a food grade surface.

The heat exchange efficiency of the evaporator 50 comprising arelatively large number of refrigerant flow channels, each having arelatively small hydraulic diameter, is significantly higher than thatof prior art evaporators described herein before. Heat exchange isincreased in part due to the increase in the effective heat transferarea between the refrigerant and the inner tube 30 due to the fins 52flanking the channels 53 and in part due to the increased heat transfereffectiveness associated with the very small hydraulic diameter flowpassages defined by the respective channels 53.

FIG. 8 illustrates a heat exchanger 100 in an alternate embodiment. Heatexchanger 100 is similar to that shown in FIGS. 4-7, and includes aninner tube 30 having fins 52 defining channels 53 and an outer tube 40.In FIG. 8, the outer tube 40 is welded to the fins 52 of inner tube 30at a plurality of circumferential weld locations 102. The weld locations102 in FIG. 8 are spaced on the outer tube 40 along a longitudinal axisof the outer tube 40 and orthogonal to the longitudinal axis of theouter tube 40. Weld locations 102 may be equally spaced or non-equallyspaced. Weld locations 102 join the inside surface of the outer tube 40to a distal end of fins 52. Headers are welded to outer tube 40 to forma pressure tight assembly. Exemplary types of welding that may be usedinclude resistance welding, electron beam welding, or laser beamwelding.

FIG. 9 illustrates the heat exchanger 100 in an alternate embodiment. Asshown in FIG. 9, weld locations 104 are located on a helix traversingthe outer tube from a first end of the outer tube 50 to a second end ofthe outer tube 50. Multiple parallel helixes may be used. The embodimentof FIG. 9 provides an advantage that no weld locations overlap, reducingthe potential for metal fatigue caused by overlapping weld locations.

The method of making the heat exchanger 100 includes forming the innertube 30 with fins 52 using techniques described herein (e.g., extrusion,hobbing, machining). The outer tube 40 is then positioned over the innertube 30. The outer tube 40 is then welded to the inner tube 30. The weldpenetrates the outer tube 40 to fuse the outer tube 40 to a distal endof fins 52. No fusing of metal occurs at the channels 52.

By welding the inner tube 30 to the outer tube 40 along the length ofthe heat exchanger 100, the pressure carrying capability of the heatexchanger 100 is greatly increased. As a result, much higher pressuresmay be achieved, or thinner walls for the inner tube 30 and/or outertube 40 may be used. From a pressure standpoint, the welded heatexchanger acts like a plurality (e.g., 128) tubes each with an innerdiameter of 1/16″. Existing designs act as an inner tube with a diameterof 3.85″ and an outer tube with a diameter of 4.6″. Hoop stress is afunction of the diameter of the pressure vessel. As an example, if theouter diameter of a pressure carrying tube is decreased from 4.6″ to0.0625″, the hoop stress is reduced approximately 30 times. This meansthat the shell may be able to hold 30 times more pressure. If needed,the strength of the headers may also be improved by adding weld pointswithin the headers.

Pressure testing has been performed on a microchannel laser weldedassembly and existing tube-in-tube assemblies. The laser welded assemblyin embodiments of the invention held more than 1,000 psi, and up to3,000 psi without failure. Existing assemblies with an inner tube and anouter tube are capable of holding in the range of 700 psi. The pressurecarrying capability of both assemblies is dependent on design (diameter,length, and wall thickness) and material used.

By improving the pressure carrying capacity of the heat exchanger 100, anumber of benefits are realized. Heat exchanger 100 may use lessmaterial than existing designs to support the same pressurerequirements, resulting in a lower material cost. Furthermore, higherpressure refrigerants (e.g., carbon dioxide) may be used to improveefficiency. The welded heat exchanger 100 also allows the heat exchangerto sustain pressures experienced when the heat exchanger is used forheating in a reverse gas mode. There are situations where it isdesirable to heat the food product in heat exchanger 100 to reducebacteria. Existing systems use electrical resistance heating or hot gasheating to heat the food product (e.g., to 150 F). The welded heatexchanger 100 may be used as a condenser in reverse gas applications toheat the food product more efficiently.

The terminology used herein is for the purpose of description, notlimitation. Specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as basis for teachingone skilled in the art to employ the present invention. While thepresent invention has been particularly shown and described withreference to the exemplary embodiments as illustrated in the drawing, itwill be recognized by those skilled in the art that variousmodifications may be made without departing from the spirit and scope ofthe invention. Those skilled in the art will also recognize theequivalents that may be substituted for elements described withreference to the exemplary embodiments disclosed herein withoutdeparting from the scope of the present invention.

Therefore, it is intended that the present disclosure not be limited tothe particular embodiment(s) disclosed as, but that the disclosure willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A heat exchanger comprising: an inner tubeextending longitudinally along a central axis and having an innersurface bounding a product chamber and an outer surface having aplurality of channels disposed at circumferentially spaced intervals inalternating relationship with a plurality of fins about thecircumference of the outer surface of the inner tube; and alongitudinally extending outer tube disposed coaxially about andcircumscribing the inner tube in radially spaced relationship, the outertube having an inner surface contacting the plurality of fins of theinner cylinder, the outer tube being welded to the fins at a pluralityof weld locations; wherein the plurality of weld locations follow asubstantially helical path, the helical path extends along the outertube from a first end of the outer tube to a second end of the outertube.
 2. The heat exchanger of claim 1, further comprising: an inletheader defined by a first recess formed in and extendingcircumferentially about the outer surface of the inner tube at a firstend of the inner tube; and an outlet header defined by a second recessformed in and circumferentially extending about the outer surface of theinner tube at a second end of the inner tube; wherein each channel ofthe plurality of channels defining a heat exchange fluid flow passageextending between the inlet header and the outlet header.
 3. The heatexchanger of claim 1, wherein the inner tube and the outer tube arecylindrical.
 4. The heat exchanger of claim 1, wherein each channel ofthe plurality of channels extends longitudinally in parallelrelationship to the axis of the inner tube.
 5. The heat exchanger ofclaim 1, wherein the plurality of channels are disposed atcircumferentially equally spaced intervals about the circumference ofthe inner tube.
 6. The heat exchanger of claim 1, wherein the pluralityof channels are machined into the outer surface of the inner tube. 7.The heat exchanger of claim 1, wherein the weld locations are spacedcircumferentially about the outer surface of the outer tube andorthogonal to the central axis.
 8. The heat exchanger of claim 1,wherein the heat exchanger withstands a pressure of 1000 psi to 3000psi.